I found a way to save money!
I recently returned from a trip to Tennessee and learned something that I want to pass on. We originally rented one car for 4 adults and a baby, and after packing in the luggage, we found the car was just too small. An upgrade was going to cost an additional $40 per day, so I headed out to every rental car booth to inquire if they had cars for rent without a reservation. Everyone told me they had plenty of cars, but without an appointment, no cars were available except for two cars which would run us $89 per day.
I then had a real honest rental gal who felt bad for us and began whispering to us. She asked if I had a cell phone with internet access. When I told her yes, she said to sit at the couch about 5 feet away, type in Travelocity, and book a car through them. I got on the site which listed every car by price range, and found Advantage was the cheapest, running $18 per day. I ordered a car with just my e-mail address, pushed the confirmation button, and immediately walked to the counter. They asked for my e-mail address and was surprised my conformation was already on their computer. The money transaction was conducted at the counter, and walked away for a car for two full days for $50.54 (had to include airport taxes). Considering a walk up was going to run ~$200, I saved $150 just by using my Droid.